1. Field of the Invention
This invention relates to an improvement in a process for producing hydrogen cyanide which comprises reacting methane or a gas containing methane as a main component, ammonia and an oxygen-containing gas, and to an apparatus for use in the process.
2. Description of the Prior Art
Hydrogen cyanide has previously been used mainly as a material for methacrylic esters or for various organic syntheses, and recently as a material for the production of sodium cyanide which is used for metal refining. Its use in the production of pharmaceuticals such as biologically active substances has also increased.
Industrial production of hydrogen cyanide involves the decomposition of formamide or the ammoxidation of methane. Hydrogen cyanide is also produced as a by-product in the production of acrylonitrile by ammoxidation of propylene.
Production of hydrogen cyanide by ammoxidation of methane is described, for example, in Japanese Patent Publication No. 14128/1960. It is obtained by reacting a gas containing methane as a main component, such as natural gas, with a gaseous mixture of ammonia and air in the presence of a platinum-type catalyst at a temperature of as high as more than 1000.degree. C. In order to prevent decomposition of hydrogen cyanide in the reaction gas in this reaction, the reaction gas at a high temperature should be quenched to below 700.degree. C. within a short period of time, and it is the general practice to inject quenching water into a site just below the catalyst bed. This method of quenching the high-temperature gas is not desirable because a large amount of thermal energy derived from a temperature of about 1000.degree. C. is lost.
U.S. Pat. No. 3,104,945 discloses a method of curtailing the consumption of energy in such a hydrogen cyanide producing apparatus. According to this method, the starting gas is pre-heated to 400.degree. to 525.degree. C. and then introduced into the reactor so that the conversions of methane and ammonia to hydrogen cyanide and the yield of hydrogen cyanide are increased.
I&EC PROCESS DESIGN AND DEVELOPMENT, Vol. 7, No. 1, pages 53-61 (1968) formulates the relation among the yield of hydrogen cyanide, the mole ratio of the starting materials, and the reaction temperature, and gives a flow chart showing that the reaction gas is directly cooled with quenching water and then cooled by using a heat-exchanger.